Dynamo Regulator Charger Circuit for full-time lights...

Discussion in 'Electrical' started by loquin, Mar 12, 2008.

  1. loquin

    loquin Active Member

  2. gone_fishin

    gone_fishin Guest

    man...somebody please box that one up and sell it :)

    good find, lou :cool:
  3. loquin

    loquin Active Member

    Well, I've been doing some digging over at the texas instrument semiconductor site, augi. They have a single-chip SLA (sealed lead acid) charger integrated circuit that would work in place of the complicated circuitry at the link above, and the electronics part count would drop to about 11 parts. About 6 small resisters, a couple of capacitors, an inductor, a transistor, and the IC. The whole circuit could fit on a pc board about 1.5 inches by 3 inches...
  4. bennyboy

    bennyboy New Member

    would you mind posting the required parts I would be interested in building this myself really what that is doing is giving you a constant a/c current you get that up to a constant 12v a/c and you might as well just slap a radio and a cigarrette lighter on your bike so you can charge your cell phone as you drive around. Im sure those generators are so smooth that being motorized would be more than capable to run a full 12 volt system that would be wonderful.
  5. Zev0

    Zev0 Member

    Geeze, I'm already waiting in line to buy. :grin:
  6. loquin

    loquin Active Member

    I haven't done the design for a 6V unit yet. But, the SLA charger IC has three different charging modes you can configure. Plus bells & whistles (LED feedback, for instance) if you wanted to include it. The basic configuration uses an external transistor to pass the DC power to the battery, a bridge rectifier & capacitor for the AC-DC conversion, three small resistors in the feedback circuitry, a choke and and a blocking diode. The IC monitors the battery voltage/internal resistance for an initial fast charge and then a trickle charge when the fast charge is done. Thus, no damage to the battery due to overcharging.

    In the next couple of weeks, I'll go through the design process and post a circuit schematic & parts list.

    The real issue is that the bicycle dynamos are low power. Only 3 watts. (Now, they WILL put out up to 6 watts at higher speeds, but, you should only count on 3 watts.) In addition, when the bike stops, the hub (or wheel driven) dynamo's output also stops. Using a transformer or voltage doubler to achieve 12 volts will not increase the amount of power they can deliver - it is still limited to 3 watts.

    Because of this, the ideal configuration for these devices would be to have them charge a small battery - one which could be used to provide power to a 3 W light for an hour or two on its own. While driving the bike during the day, all the power could be used to recharge the battery. At night, any power not used to drive the lights could also be used to maintain charge. It appears that the TI SLA battery charger IC would fit the bill perfectly for our needs.

    I've located a small (4 x 2.5 x 7/8 inch) 6V, 1.2 amp-hour sealed lead-acid battery, available from multiple sources. It would provide 6V, 3W for about 2.5 hours. As I mentioned in another thread, I believe you could modify a 3 W LED 2 or 3 Cell Mag-lite to be a very nice headlight. (Even IF you drew slightly more than 3 watts from the battery, there should be enough excess capacity in a normal driving routine to maintain a charged battery.)

    I would like to design, then build a lighting and battery charging circuit, using the Sturmey-Archer X-FDD Front Brake/Dynamo hub (which I ordered over the weekend). I'll eventually do this, and document the project here.

    The problem I'm having on the home front is that we're trying to get our house ready to go on the market for a possible move... So, most of my spare time is taken up with that for a while. So, I can't jump on this thing the way I'd really like to...:-|
  7. BSA

    BSA Guest

    Apparantly on Sheldon Browns website he just shoved the dynamo's output through a bridge diode and strait into a lead acid battery.

  8. loquin

    loquin Active Member

    Yes - you can do that. And, it will work OK... for a while. The battery itself will act as a regulator to a certain extent, as it will limit the output voltage to the maximum cell voltage. However, the dynamo current will continue to feed into the battery, even after it is fully charged, and this will lead to early battery failure.
  9. BSA

    BSA Guest

    I never thought of that. I guess that sturmey archer x-fdd kills two birds with one stone, good braking and a good power source. i'm staying tuned to this project.

  10. Nerobro

    Nerobro Member

    And if you really are kinky, you can spend $9 on a bridge rectifier and a 12v regulator. Problem solved ;-)
  11. loquin

    loquin Active Member

    No, not really.

    First, automotive regulators work by adjusting the field voltage of the alternator. Plus, with watts to burn, they're woefully inefficient.

    Second, with most Dynamos generating 6 V, not 12, the output is insufficient to charge a 12 V battery.

    Finally, a simple voltage regulator circuit makes a lousy battery charger circuit. A battery charger circuit will charge at a high voltage (and resulting current) until the battery voltage indicates that it is approaching a full charge, at which time the charger will shift over to a trickle-charge mode, to avoid damaging the battery.
  12. Nerobro

    Nerobro Member

    I come from the world of motorcycles. 3/4 of the motorcycles out there use a shunt regulator.

    Cars, bikes, both do not have battery charging circuts per-se. They use a regulator to maintain system voltage. In the case of a car, yes, they adjust field coil voltage to maintain system voltage. Usually at a high enough level to charge the battery at a sane rate, and not so high as to boil off electrolyte at a speed that the battery caps can't turn it back into water.

    What I hadn't remembered was that sticky little fact that dynamos put out **** for voltage. IIRC they only really output something like 6w. (it doesn't matter how you convert it, that is all you get) You'd be better off with a small DC motor, or even a stepper motor attached to the motors crankshaft and have that feed a linear reg, or shunt reg.

    Using a nema23 stepper motor I was able to produce considerable power at some remarkably low rpm.

    My answer came out as that's my general solution when I have "any kind" of a/c voltage source.

    Find a higher voltage dynamo, alternator, or even small DC motor. We can make more of it.
  13. loquin

    loquin Active Member

    Yes, you could use a separate generator, with a shunt regulator. But why? A bike dynamo, properly 'managed,' DOES supply enough amp-hours to light the way for you, as does a "white wire" system. The trick is using the available power - in managing it efficiently.

    An unmanaged bike dynamo really has nearly zero power to waste. However, we should also keep in mind that our motors don't have a much power to waste, either. A 50-70 watt dynamo, equivalent to a typical motorcycle output, would suck up 5 to 10 percent of the total engine output...:( No matter what we use, it has to be fairly efficient. A shunt regulator works by shunting the excess power through a big resistor to ground, and the extra load causes the generator voltage to drop to a point which won't overcharge the battery (in effect, going into a 'trickle charge' mode.) However, this wastes the excess power as heat. But, even a motorcycle, with an undersized (compared to an auto) generator, has watts to throw away, as compared to a bicycle engine.

    However, the focus of this thread is use the power that is available in a bike dynamo efficiently, for our lighting, as opposed to slapping a separate generator on the bike, and, in the process, wasting a noticeable fraction of our total engine power.

    Keep this in mind, too. A bike dynamo is rated at 3 W. This rated power output is at a speed of 12-15 km per hour bicycle speed, or at about 10 miles per hour. At 20 MPH, a bike dynamo produces about 6 watts. Although STILL not a lot of power, it DOES give us more leeway in the design. So, if I can average 20 MPH on a 10 mile trip, and am using efficient LED lighting, rated at 3 watts, I will end up with an 'overage' of 1.5 watt-hours for the trip. That extra 1.5 WH is more than enough to power the regulator circuitry, and to maintain the battery.
    Last edited: Mar 21, 2008
  14. Nerobro

    Nerobro Member

    3w doesn't go very far. Even with LED's.

    As I understand it, the white wire system is exactly the same system used on a motorcycle. You have the permanant magnet from the stator swinging by the ignition (and potentially the lighting) coils.

    against the tire bike dynamos waste a lot of power merely deforming the rubber of the tire, and of it's drive wheel. After using those on my bicycle, I decided I"d never use one again. They're just that bad.

    There are hub dynamos as well. Those have signifigantly less drag.

    Using a crankshaft mounted electrical generation system takes the most "losses" out of the line. And given the consturction of these motors, putting a stepper on the crankshaft should be simple.
  15. loquin

    loquin Active Member

    The cheap tire dynamos are bad. They're inefficient. But, they don't lose a lot of power because of the deformation of the tire (they only push against the tire with a force of about a pound.) They lose the power because they're only about 15-25 percent effecient at converting work to electricity. So, the three watts electrical power needs about 15 to 30 watts of mechanical power to make it.

    However, newer designs of tire dynamos are in the 70% efficiency range. Which is quite acceptable. Hub dynamos are in the 85% efficiency range. And, they are completely protected from mud and road grime.

    Now. As far as the three watts go.

    First. The Mag Lite LED is a three watt LED. It is powerful. And it is focusable. Three watts can work quite well, given the right optics and LED.

    Second. I talked about power management, above. Use a small sealed lead-acid battery. 1.2 Amp Hours. That, by itself, will keep a 3W LED burning for about 2.5 hours.

    Keep it charged up with the dynamo. As I mentioned, at MB speeds, a dynamo will put out about 6 watts. The excess power goes into the battery. That is the power management I was talking about. The system has enough power, but it comes in surges. Capture the power surges in the battery, and then spread it out as needed.
  16. duivendyk

    duivendyk Guest

    On the subject of battery chargers,looking around on the TI site, I ran across a 6.5 V chip (BQ2406*) they have, intended for portable devices using LI batteries.It has a built in PowerFet pass device.The specs look attractive, input voltage up to 18V,charge rate 1 A,output 1.5A max.All sorts of protection built in (prob needed!).You can get a 6V ,5.3AH (32.5 WH) battery pack for around $50.All you need is a bridge rectifier &input cap.Looks like a winner to me,JJ
  17. loquin

    loquin Active Member

    Unfortunately, that 6.5V is the input voltage over-voltage limit for that chip - not the charge voltage. It's used in PDA/Cell phone chargers, for a 4.5 volt power pack with an internal thermistor for charge feedback (the battery starts heating up when it is charged to capacity, so by monitoring the temp, the IC charger knows when to stop charging...

    There are some other TI power management ICs that look interesting. A 4 AA NiMH pack, at 2 AH or greater, would be a nice alternative to the 6V 1.2AH SLA battery...

    One of the difficulties is that when you start USING the battery while its being charged, it causes the voltage to drop a bit, and it affects how the charger IC operates. There's a couple of work-arounds that may work, but the simplest approach seems to be adding a thermistor to what ever batter pack you use, and monitor it, looking for a 'rapid' temperature rise while charging.
    Last edited: Apr 9, 2008
  18. jtmiyake

    jtmiyake Member

    bringing this thread back

    Has anyone figured out a battery / dynamo hub power system. Wouldn't a lawn mower or scooter acid battery work without all the complicated circuitry? I have a Sturmey Archer XFDD hub being laced and I am trying to figure out a full time light system.
  19. duivendyk

    duivendyk Guest

    You could charge a 6V battery with a 4 diode bridge rectifier circuit (preferably Schottky diodes) and stick a 7V 2Watt zener diode across it to prevent overcharging and/or a bunch of 2x 3.5 V LED's in series/parallel.When the LED's begin to light up,the battery starts getting overcharged.That's not all that complicated.
    Last edited by a moderator: Jun 5, 2009
  20. HoughMade

    HoughMade Guest

    What are your thoughts about a similar setup for 12v?